The present invention relates to an improvement for a self lubrication type solid lubricating rolling bearing used under a circumstance such as at high temperature, in vacuum or at high temperature in vacuum for which grease lubrication can not be adopted.
For rolling bearings used under a circumstance such as at high temperature, in vacuum or at high temperature in vacuum for which grease lubrication as a general lubrication system can not be adopted, bearing lubrication of a solid lubricating system has been conducted so far. In the existent solid lubrication rolling bearing, it has been considered in an early stage to prepare a crown type cage by a solid lubricating material as a lubricant supply source. However, the solid lubricating material is extremely fragile and sometime suffers from cracking or chipping during assembling of bearings. In view of the above, a spacer type solid lubricating bearing in which a cage is separated and disposed between each of rolling elements has been considered. Various methods have been proposed as a method of assembling spacers in the spacer type solid lubricating bearings and, for example, Japanese Unexamined Patent Publications Nos. 7-151,152 and 9-144760 disclose a method of inserting a spacer from an insertion recess disposed to a portion of a bearing. Further, Japanese Unexamined Patent Publication No. 8-4773 discloses a method of inserting a cylindrical spacer from a portion between inner and outer rings vertically in a circumferential direction and, at the same time, sealing the portion between the inner and the outer rings by a shield in a rolling bearing.
Further, Japanese Utility Model Publication No. 7-21927 discloses a cage for a rolling bearing in which a concave portion as a pocket capable of containing at least two rolling elements is formed, and a graphite spacer is interposed between the rolling elements contained in each pocket.
In the spacer type solid lubricating bearing in which the recess for the insertion of the spacer is disposed to a portion of the bearing as disclosed in the publication described above for incorporating the spacer, not only the fabrication cost increases, but also the inserted spacer is caught by the recess to hinder the rotation and, accordingly, sometimes causes abnormal vibrations. Particularly, in a case where an axial load exerts on the bearing, since the rolling face approaches the recess, abnormal vibrations tend to be generated to bring about a problem that the spacer is dropped depending on the case.
Further, when the solid lubricating spacer is interposed between each of the rolling elements, the number of the spacers required for one shaft is increased to increase the cost, as well as a circumferential impact caused to the spacer during rotation is increased to bring about a problem of injuring the spacer.
Particularly, even if a special cage is used, when a material comprising graphite is used as a main ingredient for the spacer to be interposed between the rolling elements, the spacer is abraded rapidly and a circumferential gap is remarkably increased in the cage to result in a problem that no sufficient effect can be obtained for extending the service life. Further, in such an application use where a high load exerts on the spacer, the spacer is sometimes destroyed to result in a problem also in view of reliability. Further, since the lubricating performance of graphite is degraded in vacuum, the bearing life is limited when used in vacuum.
In view of the above, it is an object of the present invention to provide a solid lubricating rolling bearing of a high reliability at a reduced cost with no hindrance to rotation caused by interference of a spacer, free from the worry of dropping of the spacer, and capable of attaining smooth and safe rotation with less vibrations.
The present invention relates to a solid lubricating rolling bearing capable of attaining such an object.
The solid lubricating rolling bearing according to the present invention has an inner bearing, an outer bearing, rolling elements, spacers made of a material containing a solid lubricant, and a cage with a pocket for accommodating at least one spacer and one rolling element as a unit. With such a constitution, the solid lubricating rolling bearing of the present invention needs no recess for incorporating a spacer. Therefore, fabrication cost for the existent recessed portion can be reduced to lower the cost and no abnormal vibrations are generated since the inserted spacer is not caught to the recessed portion and does not hinder the rotation. In addition, since the inserted spacer is constrained by rolling elements on both sides, it is free from the worry of detaching and dropping out of a race way groove of inner and outer rings due to vibrations. In addition, in view of the lubricating performance, since all rolling elements are in contact each at least at a portion thereof with the spacer containing the solid lubricant, and the solid lubricant transfers and deposits (transfer deposition) to the contact face of the rolling element, satisfactory lubricating performance can be obtained by the solid lubricant.
Further, in the solid lubricating rolling bearing according to the present invention, since the cage is constituted as a cage accommodating two rolling elements for putting the spacer therebetween as a unit, the number of spacers can be decreased to one-half the number of rolling elements, so that the cost can be reduced, as well as the circumferential impact caused to the spacer during rotation of the bearing is decreased to suppress the injury of the spacer, since two rolling elements and one spacer are accommodated as one unit in a pocket of the cage, compared with the existent cage in which rolling elements and spacers are combined each by an identical number.
Further, in the solid lubricating rolling bearing according to the present invention, since the size of the circumferential clearance of the pocket in the cage is defined within a range from 0.01 mm to 20% for the diameter of the rolling element, the bearing torque and vibrations of the cage can be suppressed effectively.
Further, in the solid lubricating rolling according to the present invention, since the diameter of the spacer is defined as 0.50 to 0.95 times the diameter of the rolling element, it is possible to suppress the rotation torque thereby preventing localized abrasion and keeping the vibration level low.
Further, in the solid lubricating rolling bearing according to the present invention, since the radius of curvature for the pocket of the cage at the contact face with the rolling element is defined as from 1.01 to 1.10 times the radius of the rolling element, an appropriate clearance is between the cage and the rolling element to prevent vibrations of the cage.
In the solid lubricating rolling bearing according to the present invention, since the material for the spacer is made of a self-lubricating sintered composite material comprising one of molybdenum disulfide, tungsten disulfide or boron nitride, or molybdenum disulfide and tungsten disulfide as a main ingredient of a lubricant and obtained by sintering the ingredient for the lubricant together with a metal selected from Fe, Cu, Ni, W. Sn and Cr or an oxide, a nitride and a boride thereof, it is possible to prevent occurrence of excess abrasion dusts or cracking of the spacer. Particularly, the self-lubricating sintered composite material comprising 80% or less of a lubricant ingredient that comprises molybdenum disulfide and tungsten disulfide as the main ingredient and the balance of an Fe series alloy has higher strength compared with those comprising graphite as the main ingredient, shows appropriate abrasion amount, can be used both in atmospheric air and in vacuum and is suitable to the bearing of the present invention. However, when the bearing of the present invention is used at a temperature of 350xc2x0 C. or higher, a self-lubricating sintered composite material having a lubricant mainly comprising boron nitride and Ni alloy in combination is more suitable to the spacer material.
The solid lubricating rolling bearing according to the present invention can be used suitably, for example, as a bearing for supporting axles of a Kiln car used at a high temperature and at a low speed.